1. Field of the Invention
The instant invention pertains to a planetary transmission, and particularly to a lubrication system for the planetary transmission. The planetary transmission is mounted in a rear wheel of a mining or construction vehicle, and is used for transferring engine power to the wheel for vehicle movement. Adequate lubrication of thrust washers in this transmission is essential to prevent transmission failures and limit vehicle downtime.
2. Description of Related Art
A conventional planetary transmission and lubrication system therefor is shown in FIGS. 1 and 2. As shown in FIG. 1, a motor 1 drives a shaft 2. At a distal end of the shaft 2 is provided a first gear set 3 and a second gear set 4 of the planetary transmission. The planetary transmission serves to rotate ground engaging wheels 50, which are supported by a wheel hub.
As shown in FIG. 2, gear set 3 includes a carrier 8, a high speed sun gear 11, high speed planetary gears 12a–12c, and a high speed ring gear 13. The high speed sun gear is provided on an outer circumference of the shaft 2, via a splined connection or being welded thereto, so as to be non-rotatable relative to the shaft such that it rotates at the same speed as does the shaft. Surrounding the sun gear 11 and meshing therewith are the planetary gears 12a–12c. The high speed planetary gears 12a–12c are connected to the carrier 8 and supported via needle or roller bearings 7. Surrounding the high speed planetary gears 12a–12c is the ring gear 13 which meshes with the high speed planetary gears. The high speed ring gear 13 is fixed to frame 5 via bolts 6 so as to be non-rotatable.
With further reference to FIG. 2, gear set 4 includes a carrier 9, a low speed sun gear 21, low speed planetary gears 22a–22d, and a low speed ring gear 23. Surrounding the sun gear 21 and meshing therewith are the planetary gears 22a–22d. The low speed planetary gears 22a–22d are connected to the carrier 9 via needle or roller bearings 14. Surrounding the low speed planetary gears 22a–22d is the ring gear 23 which meshes with the low speed planetary gears. The low speed ring gear 23 is fixed to the high speed ring gear 13 via a splined connection so as to be non-rotatable relative thereto. The carrier 8 is splined to the low speed sun gear 21.
As shown in FIG. 2, a circumferential torque tube 19 is fixed to the carrier 9 via bolts 18, and is also fixed to wheel hub 16 via bolts 17. The wheel hub 16 is rotatably supported on the frame 5 via bearings 51, and accordingly, the wheel hub 16 rotates with the carrier 9 and the circumferential torque tube 19. An opening 24 is provided at a central portion of the carrier 9, which opening is aligned with a rotational axis of the shaft 2.
A plug 25 includes a first portion received within and fixed to the high speed sun gear 11, such that the plug is non-rotatable relative to the high speed sun gear. The plug 25 also includes a second portion that is received within the low speed sun gear 21 to support an inboard thrust washer 27. The second portion of the plug 25 is loosely received within the low speed sun gear 21 such that the plug, and thus the high speed sun gear 11, are rotatable relative to the low speed sun gear. The plug 25 also includes a cylindrical flange 26 between the first and second portions.
A loosely mounted retainer 15 surrounds the plug 25 and is positioned between the flange 26 and an end the low speed sun gear 21. The retainer 15 serves to maintain a proper position of the carrier 8 and the low speed sun gear 21. The inboard thrust washer 27 is positioned between the retainer 15 and the flange 26 of the plug 25. The inboard thrust washer is loosely mounted to the plug 25.
Attached to the carrier 9 via bolts 29, and covering opening 24, is a cover 28. The cover 28 defines a cylindrical recess on an inner surface thereof. Positioned within this recess between an opposite end of the low speed sun gear 21 and the inner surface of the cover 28 is an outboard thrust washer 30.
As is seen in FIG. 2, a passageway 39 extends through the low speed sun gear 21 from a root portion of the teeth to a hollow interior of the low speed sun gear.
In operation, upon actuation of the motor 1, shaft 2 is rotated at a high speed. Because the high speed sun gear 11 is splined or welded to the shaft 2, the high speed sun gear rotates with the shaft at the same rotational speed. Rotational output of the shaft 2 is transmitted to the high speed ring gear 13 because of the meshing arrangement of the high speed sun gear and the high speed planetary gears 12a–12c, and the meshing arrangement of the high speed planetary gears and the high speed ring gear. Because the high speed ring gear 13 is fixed to the frame 5, and because the high speed planetary gears 12a–12c are connected to the carrier 8, the rotational output of the shaft 2 results in rotation of carrier 8. Rotational output of the carrier 8 is transmitted to the low speed sun gear 21 due to the splined connection between the low speed sun gear and this carrier.
Then, because of the meshing relationship between the low speed sun gear 21 and the low speed planetary gears 22a–22d, and because of the meshing relationship between the low speed planetary gears and the low speed ring gear 23, rotational output of the low speed sun gear is transmitted to low speed ring gear. Because the low speed ring gear 23 is splined to the high speed ring gear 13, and because the high speed ring gear is fixed to the frame 5, the low speed ring gear is also rotationally fixed. Accordingly, because the low speed planetary gears 22a–22d are connected to the carrier 9, rotational output of the low speed sun gear 21 results in rotation of carrier 9. And, because of carrier 9 being bolted to circumferential torque tube 19, which in turn is bolted to wheel hub 16, rotation of carrier 9 results in rotation of the wheel hub 16 at a reduced speed relative to the rotational speed of the shaft 2.
As should be clear from the above description, the low speed sun gear 21 rotates relative to the plug 25, and accordingly, the inboard thrust washer 27 is subject to frictional forces which can result in wear, overheating and breakage of this washer if not sufficiently lubricated. Similarly, the carrier 9, and thus the cover 28, rotates at a slower speed than does the low speed sun gear 21, and accordingly, the outboard thrust washer 30 can also be severely damaged if not sufficiently lubricated.
In order to lubricate the thrust washers 27 and 30 oil is forced through passageway 39. Upon entering the hollow interior portion of the low speed sun gear, through passageway 39, the oil lubricates the thrust washers 27 and 30. However, because of the arrangement of passageway 39, a sufficient amount of oil is not always conveyed to the thrust washers such that they are not sufficiently lubricated and become excessively worn.